The present invention relates to a modified polyvinyl acetal resin, a modifier for curable resins, a curable resin composition, and laminated products.
The modified polyvinyl acetal resin of the present invention is excellent not only in dielectric characteristics but in compatibility with various solvents and thermosetting resins and in adhesiveness. The resin is hence useful as an electrical insulating material.
The modifier for curable resins of the invention comprises the specific modified polyvinyl acetal resin. By adding this modifier to a curable resin, a curable resin composition can be provided which has excellent adhesiveness and is suitable for use as an electrical insulating material, etc.
The curable resin composition of the invention comprises a curable resin/curing agent combination compounded with a specific modified polyvinyl acetal resin. The composition has greatly improved film-forming properties and can hence be applied to various substrates to form a stable, homogeneous film. Since the film combines excellent adhesiveness to substrates and flexibility, the composition is especially suitable for use as an adhesive.
The laminated products of the invention comprise a substrate layer and a layer of a curable resin composition containing a specific modified polyvinyl acetal resin and/or of a cured composition obtained by curing the curable resin composition. Since the layer of the curable resin composition has greatly improved film-forming properties, it can be applied to various substrates to form a stable, homogeneous film, which combines excellent adhesiveness to the substrates and flexibility. The laminated products are hence used especially as adhesives having excellent flexibility and high adhesiveness.
Curable resins, which mostly comprise low-molecular weight compounds, are applied in the form of a solution in a solvent or in a melt form to substrates and then cured under given conditions to thereby exhibit adhesiveness to the substrates. As a result, satisfactory laminated products can be obtained. Furthermore, by superposing an adherend on the surface of the thus-applied solution or melt of an uncured curable resin and then curing the resin, a three-layer laminated product composed of the substrate, an adhesive layer, and the adherend can be obtained in which the resin exhibits adhesiveness to the adherend and which also is satisfactory. Besides being used in such applications, curable resins are extensively used as matrix resins in an application in which fibers or an inorganic or organic filler is mixed with a solution or melt of the curable resin and the mixture is cured alone to obtain a satisfactory composite, or in an application in which the mixture is likewise applied to a substrate and united with an adherend.
In the case of using a solid curable resin, a solution prepared by dissolving the resin in a solvent is applied to a substrate and the solvent which has become unnecessary is removed thereafter to form an exceedingly hard film. However, because the resin has a low-molecular weight, the film is highly brittle and is apt to readily peel off the substrate or develop cracks. In the case of using a liquid curable resin, a solution thereof is prepared and applied in the same manner and the solvent is then removed. In this case, however, there are many problems, for example, that the resin, upon solvent removal, returns to the original liquid state and, as a result, it becomes difficult to maintain an even film thickness, making it difficult to exhibit even and stable adhesive strength, and that the resin surface has tackiness and this necessitates significantly complicated operations. Because of these drawbacks, a technique is used in which the curing reaction is caused to proceed to some degree to thereby increase the molecular weight of the resin, i.e., bring the resin into the so-called B-stage. Although this technique is effective in improving evenness of film thickness, it is difficult to control the B-stage and to stably maintain the B-stage over long. In addition, as the molecular weight increases, the ability to wet an adherend decreases, resulting in reduced adhesion strength. Consequently, this technique is not a satisfactory technique for improvements.
In contrast, an attempt has been made to maintain applicability and film properties without increasing the molecular weight of a curable resin as a whole, by adding thereto a rubber, thermoplastic resin, etc. However, curable resins do not always have satisfactory compatibility with rubbers or thermoplastic resins. There are cases where even though the composition has been homogenized with a solvent, it undergoes phase separation upon solvent volatilization, or undergoes phase separation upon curing reactions after solvent vaporization and coagulates at the composition/substrate interface or, conversely, at the composition/air interface, resulting in an insufficient effect of improvement.
One measure in overcoming the problem described above is proposed, e.g., in JP-A-5-186667 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d), which is an epoxy resin composition comprising an epoxy compound, a curing agent, and a polyvinyl acetal resin having a peculiar structure highly compatible with the epoxy compound/curing agent combination.
However, this epoxy resin composition was found to have drawbacks that application of the composition to a substrate results in cissing on the substrate surface and that curing the applied composition significantly reduces the flexibility of the substrate.
On the other hand, various insulating materials are known for use in the field of electronics industry as overcoat materials, interlayer dielectric materials, or the like in semiconductors, ICs, hybrid ICs, wiring circuit boards, display devices, display parts, etc. Examples thereof include passivation films, soldering resists, plating resists, interlayer dielectric materials, and moisture-proof protective films. These insulating materials also have come to be desired to have higher performances and higher reliability with the recent trend in electronic parts toward miniaturization, weight reduction, density increase, and speed increase.
In order for an insulating material to have a smaller dielectric loss, even in a slight degree, it should have a lower dielectric constant and a smaller dielectric loss tangent.
As such materials are used thermosetting resins such as phenolic resins, epoxy resins, and polyimide resins and thermoplastic resins such as fluororesins and polyolefin resins.
However, these thermosetting resins have had difficulties in attaining higher speeds and higher reliability because they usually have a dielectric constant as high as 4.0 or higher and a dielectric loss tangent as large as 0.01 or above.
The thermoplastic resins, on the other hand, have had problems, for example, that they have poor workability, poor adhesiveness, and insufficient reliability.
Objects of the invention are (i) to provide a modified polyvinyl acetal resin excellent in dielectric characteristics and in compatibility with thermosetting resins and adhesiveness, (ii) to provide a modifier for curable resins which has excellent compatibility with curable resins and which, when added to a curable resin, improves the dielectric characteristics, film-forming properties, and flexibility of the resin, (iii) to provide a curable resin composition in which the modified polyvinyl acetal resin has excellent compatibility with the curable resin and which is excellent in film-forming properties and flexibility and adhesiveness, and (iv) to provide a laminated product in which a stable and even film having excellent adhesiveness to the substrate can be formed and which has flexibility.
The present inventors made intensive investigations in view of the circumstances described above. As a result, they have found that (i) a modified polyvinyl acetal resin having a specific structure is excellent not only in dielectric characteristics but in compatibility with various solvents and thermosetting resins and in adhesiveness, (ii) addition of this modified polyvinyl acetal resin to a curable resin improves the dielectric characteristics and film-forming properties of the curable resin, (iii) by incorporating a specific modified polyvinyl acetal resin to a combination of a curable resin and a curing agent, a cured resin is obtained which is excellent in film-forming properties, flexibility, and adhesiveness, and (iv) a laminated product comprising a substrate and an adhesive layer comprising a curable resin composition containing the modified polyvinyl acetal resin is excellent in substrate wettability and adhesiveness after cure while retaining the intact flexibility of the substrate. The present invention has been completed based on these findings.
The essential aspects of the present invention reside in a modified polyvinyl acetal resin consisting essentially of repeating units represented by the following formula (I): 
wherein R1 represents an optionally substituted aryl group, an optionally substituted aralkyl group, or an optionally substituted alkenyl group having an optionally substituted aryl group; R2 represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms; R3 represents an optionally substituted, bivalent hydrocarbon group having 1 to 20 carbon atoms; and a, b, c, d, and e indicate the proportions in mol % of the respective structural units in the formula and satisfy 0 less than axe2x89xa685, 0xe2x89xa6bxe2x89xa680, 0xe2x89xa6cxe2x89xa650, 0xe2x89xa6dxe2x89xa630, and 0 less than exe2x89xa650.
In a preferred embodiment of the invention, a modifier for curable resins is provided which comprises the modified polyvinyl acetal resin.
The invention further provides a curable resin composition comprising a curable resin (A) and a curing agent (B) and further containing a modified polyvinyl acetal resin (C) consisting essentially of repeating units represented by the following formula (Ixe2x80x2), and furthermore provides a laminated product comprising a layer of the curable resin composition and a substrate layer: 
wherein R1 represents an optionally substituted aryl group, an optionally substituted aralkyl group, or an optionally substituted alkenyl group having an optionally substituted aryl group; R2 represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms; R3 represents an optionally substituted, bivalent hydrocarbon group having 1 to 20 carbon atoms; and a, b, c, d, and e indicate the proportions in mol % of the respective structural units in the formula and satisfy 0xe2x89xa6axe2x89xa685, 0xe2x89xa6bxe2x89xa680, 0xe2x89xa6cxe2x89xa650, 0xe2x89xa6dxe2x89xa630, 0xe2x89xa6exe2x89xa650, and a+bxe2x89xa00.
In this specification, formulae (I) and (Ixe2x80x2) are structural formulae, each of which merely indicates the proportions of constituent elements of the resin, and are not intended to specify an arrangement of these elements (e.g., a block arrangement). The modified polyvinyl acetal resin represented by formula (I) may contain other constituent elements as long as these optional elements do not defeat the objects of the invention.
The invention will be explained below in detail.
(Modified Polyvinyl Acetal Resin)
The characteristic feature of the invention resides in a modified polyvinyl acetal resin consisting essentially of repeating units represented by formula (I). 
In formula (I), R1 represents an optionally substituted aryl group, an optionally substituted aralkyl group, or an optionally substituted alkenyl group having an optionally substituted aryl group; R2 represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms; and R3 represents an optionally substituted, bivalent hydrocarbon group having 1 to 20 carbon atoms. Furthermore, a, b, c, d, and e indicate the proportions in mol % of the respective structural units in the formula and satisfy 0xe2x89xa6axe2x89xa685, 0xe2x89xa6b80, 0xe2x89xa6cxe2x89xa650, 0xe2x89xa6dxe2x89xa630, and 0xe2x89xa6exe2x89xa650.
In the case where R1 in formula (I) is an optionally substituted aryl group, it preferably has 6 to 12 carbon atoms. Examples thereof include phenyl, tolyl, xylyl, ethylphenyl, methoxyphenyl, aminophenyl, chlorophenyl, and naphthyl.
When R1 is an optionally substituted aryl group, the resin is improved in Tg and is effective in improving heat resistance.
In the case where R1 is an optionally substituted aralkyl group, it preferably has 7 to 12 carbon atoms. Examples thereof include benzyl, phenylethyl, and phenylpropyl.
When R1 is an optionally substituted aralkyl group, the resin is especially effective in reducing dielectric loss tangent.
In the case where R1 is an optionally substituted alkenyl group having an optionally substituted aryl group, it preferably has 8 to 12 carbon atoms. Examples thereof include phenylvinyl and phenylpropenyl.
R1 is preferably an optionally substituted aryl group or an optionally substituted aralkyl group.
Examples of the substituents of these aryl, aralkyl, and alkenyl groups include alkyl groups such as methyl and ethyl, alkoxy groups such as methoxy, amino, alkylamino groups, acylamino groups, carboxyl, carboxylic ester groups, hydroxyl group, and halogen atoms such as chloro, besides the substituents given above.
In the case where R2 is an alkyl group having 1 to 10, preferably 1 to 8 carbon atoms, examples thereof include methyl, ethyl, propyl, butyl, and hexyl.
Preferred examples of R2 include methyl and propyl.
R3 is an optionally substituted bivalent hydrocarbon group having 1 to 20, preferably 1 to 12 carbon atoms. Examples thereof include methylene, ethylene, trimethylene, butylene, cyclohexylene, methylcyclohexylene, carboxycyclohexylene, norbornylene, vinylene, cyclohexenylene, phenylene, and naphthylene.
Preferred examples of R3 include ethylene, phenylene, and vinylene.
With respect to the proportions (mol %) of the structural units, that of a is 0xe2x89xa6axe2x89xa685, preferably 10xe2x89xa6axe2x89xa680; that of b is 0xe2x89xa6bxe2x89xa680, preferably 0xe2x89xa6bxe2x89xa670; that of c is 0xe2x89xa6cxe2x89xa650, preferably 0xe2x89xa6cxe2x89xa645; that of d is 0xe2x89xa6dxe2x89xa630, preferably 0xe2x89xa6dxe2x89xa615; and that of e is 0xe2x89xa6exe2x89xa650, preferably 1xe2x89xa6exe2x89xa650.
In case where a is too small, the resin has an increased dielectric constant and a lowered Tg and is hence less effective in improvements. In case where c is too large, the resin has enhanced hydrophilicity to show impaired performances due to moisture absorption, has an increased dielectric constant, and is hence less effective in improvements.
In case where d is too large, the resin has too small a proportion of acetal groups incorporated through acetalization and hence shows insufficient performances. In case where e is too small, the resin has reduced adhesiveness and is less effective in improvements. In case where e is too large, the resin has enhanced hydrophilicity to show impaired performances due to moisture absorption, has an increased dielectric constant, and is hence less effective in improvements.
In this specification, formula (I) is a structural formula which merely indicates the proportions of constituent elements of the resin and is not intended to specify an arrangement of these elements (e.g., a block arrangement). The modified polyvinyl acetal resin represented by formula (I) may contain other constituent elements as long as these optional elements do not defeat the objects of the invention.
The modified polyvinyl acetal resin represented by formula (I) generally has an acid value of from 5 to 150 mg-KOH/g as determined through the titration of a solution of 1.0 g of the resin in 200 ml of DMF with 0.5 mol/l ethanolic potassium hydroxide solution using automatic titrator GT-05, manufactured by Mitsubishi Chemical Corp.
The modified polyvinyl acetal resin of the invention is suitable for use in electrical insulating materials, and is useful in anisotropic conductive films, interlayer dielectrics, or electronic members for high-speed communication apparatus, e.g., routers. On the other hand, the modified polyvinyl acetal resin is applicable to other fields such as, e.g., adhesives, coating materials, linings, fiber-reinforced composites, and constructional materials so as to take advantage of properties thereof such as adhesiveness and film-forming properties.
Since the modified polyvinyl acetal resin is highly compatible, it can be used in combination with a curable or plastic resin, e.g., an epoxy resin, acrylic resin, or urethane resin.
Inorganic or organic fibers and organic or inorganic fillers may be added to the composition as long as this addition does not reduce the performances of the composition.
(Process for Producing Modified Polyvinyl Acetal Resin)
Processes for producing the modified polyvinyl acetal resin of the invention are not particularly limited. However, a preferred process, for example, comprises acetalizing a polyvinyl alcohol and then reacting the resultant acetalization product with an acid anhydride to esterify part of the hydroxyl groups remaining in the acetalization product with the acid anhydride and thereby modify the acetalization product.
A commercial acetalization product can be used as a starting material and modified with an acid anhydride.
The acetalization of a polyvinyl alcohol with an aldehyde can be conducted, for example, in accordance with the method described in JP-A-5-140217. An outline of this method is as follows.
The acetalization of a polyvinyl alcohol is accomplished by reacting the polyvinyl alcohol with an aldehyde represented by formula (II) and/or an aldehyde represented by formula (III) with the aid of an acid catalyst usually in a solvent.
It is preferred in this case that the water yielded by the reaction be distilled off as an azeotrope with the solvent.
The polyvinyl alcohol used as a starting material is not particularly limited, but preferably has a degree of polymerization of from 30 to 3,000. Usable examples of commercial polyvinyl alcohol products include GOHSENOL NL05, manufactured by The Nippon Synthetic Chemical Industry Co., Ltd.
The aldehydes used as starting materials are respectively represented by formulae (II) and (III):
R1xe2x80x94CHOxe2x80x83xe2x80x83(II)
R2xe2x80x94CHOxe2x80x83xe2x80x83(III)
wherein R1 and R2 are the same as in formula (I).
Examples of the aldehyde represented by formula (II) include benzaldehyde and derivatives thereof, naphthaldehydes and derivatives thereof, cinnamaldehyde and derivatives thereof, and alkylaldehydes having a phenyl or naphthyl group. In these aldehydes, the benzene and naphthalene rings may have one or more substituents selected from alkyl groups, alkoxy groups, amino, alkylamino groups, acylamino groups, carboxyl, carboxylic ester groups, hydroxyl group, and halogen atoms.
Specific examples of these aldehydes include benzaldehyde, 1-naphthaldehyde, phenylacetaldehyde, phenylpropionaldehyde, o-tolualdehyde, p-tolualdehyde, o-anisaldehyde, m-anisaldehyde, p-anisaldehyde, p-ethylbenzaldehyde, o-chlorobenzaldehyde, p-chlorobenzaldehyde, and cinnamaldehyde. Preferred of these are benzaldehyde, phenylacetaldehyde, o-tolualdehyde, and p-tolualdehyde.
The aldehyde represented by formula (II) has an aromatic ring, and incorporation of aromatic rings derived from this aldehyde enables the modified polyvinyl acetal resin to have a reduced dielectric constant, a reduced dielectric loss tangent, and an improved Tg. It can be further thought that since this modified polyvinyl acetal resin has improved compatibility with other resins, it gives, when blended with another resin, a resin composition having improved viscosity characteristics and giving a cured composition having improved impact resistance.
Examples of the aldehyde represented by formula (III) include formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, caproic aldehyde, caprylaldehyde, and capric aldehyde. Preferred of these are formaldehyde, acetaldehyde, and butyraldehyde.
In the modified polyvinyl acetal resin, a+b is preferably in the range of from 30 to 80 mol %.
Further, of the structural units represented by formula (I) of the modified polyvinyl acetal resin, it is preferred that the proportion of the structural acetal units having R1 to the sum of the structural acetal units having R1 and the structural acetal units having R2, a/a+b, is 10% or more. Too small proportions thereof result in an increased dielectric constant and a lessened effect in improvements.
As the acid catalyst is used, for example, an inorganic acid such as hydrochloric acid, sulfuric acid, or phosphoric acid, acetic acid, or p-toluenesulfonic acid. Preferred of these are hydrochloric acid, sulfuric acid, and p-toluenesulfonic acid. The use amount of the catalyst is generally from 0.005 to 0.2 mol per mol of the aldehyde(s).
The solvent is not particularly limited as long as it forms an azeotrope with water and readily separates from the water through liquid/liquid separation. Preferred examples thereof include aromatic hydrocarbons such as benzene, toluene, and xylene. Especially preferred is toluene.
The use amount of the solvent is generally from 100 to 2,000 parts by weight, preferably from 200 to 1,000 parts by weight, per 100 parts by weight of the polyvinyl alcohol used as a starting material.
The reaction temperature is generally from 20 to 90xc2x0 C., preferably from 40 to 70xc2x0 C. The reaction time is generally from 2 to 10 hours.
The reaction may be conducted either batchwise or continuously.
After completion of the reaction, the target polyvinyl acetal resin can be recovered from the reaction mixture in an ordinary way. For example, a poor solvent for the target polyvinyl acetal resin, such as methanol, is added to the reaction mixture to precipitate the resin, after the reaction mixture is neutralized and filtered after completion of the reaction. The polyvinyl acetal resin thus precipitated is recovered. According to need, the resin precipitated can be purified by repeating an operation in which the resin recovered is redissolved in a good solvent such as toluene and then precipitated again with the poor solvent.
Subsequently, the acetalization product obtained is modified with an acid anhydride. This modification can be conducted by using any known method of esterifying an alcohol. More specifically, the modification is conducted by reacting the polyvinyl acetal resin thus obtained with an acid anhydride represented by formula (IV).
The polyvinyl acetal resin obtained by the step described above is used as a feed material. However, when a commercial product of the resin is available, it may be used. The acid anhydride as the other feed material is one represented by formula (IV): 
wherein R3 is the same as in formula (I).
Examples of the acid anhydride represented by formula (IV) include phthalic anhydride, naphthalene-1,2-dicarboxylic anhydride, succinic anhydride, maleic anhydride, glutaric anhydride, trimellitic anhydride, cyclohexane-1,2-dicarboxylic anhydride, 4-cyclohexene-1,2-dicarboxylic anhydride, 4-methylcyclohexane-1,2-dicarboxylic anhydride, and norbornane-2,3-dicarboxylic anhydride. Preferred of these are phthalic anhydride, succinic anhydride, and maleic anhydride. It is thought that the addition of this acid anhydride improves compatibility with other resins and adhesiveness. Consequently, e in formula (I) is preferably 1 mol % or larger.
This reaction may be conducted without using a catalyst. However, by using a catalyst, the reaction can be carried out under milder conditions. Examples of the catalyst include tertiary amines such as pyridine, lutidine, 4-dimethylaminopyridine, triethylamine, diisopropylethylamine, and N-ethylpiperidine, bases such as sodium acetate, and acid catalysts such as sulfuric acid, hydrochloric acid, ZnCl2, and HClO4. Preferred of these are tertiary amines. The use amount of the catalyst is generally from 0.001 to 1 mol per mol of the acid anhydride.
The reaction can be conducted without using a solvent, i.e., while keeping the resin in a bulked state. In the case of using a solvent, the solvent may be a hydrocarbon, ketone, ester, ether, amide, or another solvent. Specific examples thereof include N,N-dimethylformamide, toluene, MEK, and MIBK. The use amount of the solvent is generally from 100 to 2,000 parts by weight, preferably from 200 to 1,000 parts by weight, per 100 parts by weight of the polyvinyl acetal resin as a feed material.
The reaction temperature is generally from 30 to 200xc2x0 C., preferably from 50 to 180xc2x0 C. The reaction time is generally from 1 to 15 hours.
The reaction may be conducted either batchwise or continuously.
After completion of the reaction, the target modified polyvinyl acetal resin can be recovered from the reaction mixture in an ordinary way. For example, a poor solvent for the target modified polyvinyl acetal resin, such as methanol, is added to the reaction mixture to precipitate the resin, after the reaction mixture is neutralized and filtered after completion of the reaction. The modified polyvinyl acetal resin thus precipitated is recovered. According to need, the resin precipitated can be purified by repeating an operation in which the resin recovered is redissolved in a good solvent such as acetone and then precipitated again with the poor solvent.
(Modifier for Curable Resin)
The modifier for curable resins of the invention is characterized by comprising the modified polyvinyl acetal resin consisting essentially of repeating units represented by formula (I). The modifier may contain other ingredients as long as these optional ingredients do not impair the performances of the modifier. For example, a solvent such as, e.g., methyl ethyl ketone, may be added for the purpose of mixing time reduction.
The use amount of the modifier for curable resins varies depending on purposes of the use thereof. However, too small addition amounts in terms of the modified polyvinyl acetal resin ingredient result in the reduced ability to form a film on substrates. On the other hand, in case where the addition amount thereof is too large, the resultant composition has an increased viscosity and hence the solvent volatilizes insufficiently and partly remains in the film. The residual solvent may be causative of film blistering or peeling, depending on the subsequent heat history. Consequently, the modified polyvinyl acetal resin ingredient represented by formula (I) is added in an amount of generally from 0.1 to 200 parts by weight, preferably from 0.5 to 180 parts by weight, per 100 parts by weight of the curable resin.
(Curable Resin Composition)
The curable resin composition of the invention, which comprises a curable resin (A) and a curing agent (B), is characterized by further containing a modified polyvinyl acetal resin (C) consisting essentially of repeating units represented by formula (Ixe2x80x2).
Ingredient (C) used in the invention is a modified polyvinyl acetal resin consisting essentially of repeating units represented by formula (Ixe2x80x2). 
In formula (Ixe2x80x2), R1 represents an optionally substituted aryl group, an optionally substituted aralkyl group, or an optionally substituted alkenyl group having an optionally substituted aryl group; R2 represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms; and R3 represents an optionally substituted, bivalent hydrocarbon group having 1 to 20 carbon atoms. Furthermore, a, b, c, d, and e indicate the proportions in mol % of the respective structural units in the formula and satisfy 0xe2x89xa6axe2x89xa685, 0xe2x89xa6bxe2x89xa680, 0xe2x89xa6cxe2x89xa650, 0xe2x89xa6dxe2x89xa630, 0xe2x89xa6exe2x89xa650, and a+bxe2x89xa00.
In the case where R1 in formula (Ixe2x80x2) is an optionally substituted aryl group, it preferably has 6 to 12 carbon atoms. Examples thereof include phenyl, tolyl, xylyl, ethylphenyl, methoxypheny, aminophenyl, chlorophenyl, and naphthyl.
When R1 is an optionally substituted aryl group, the resin is improved in Tg and is effective in improving heat resistance.
In the case where R1 is an optionally substituted aralkyl group, it preferably has 7 to 12 carbon atoms. Examples thereof include benzyl, phenylethyl, and phenylpropyl.
When R1 is an optionally substituted aralkyl group, the resin is especially effective in reducing dielectric loss tangent.
In the case where R1 is an optionally substituted alkenyl group having an optionally substituted aryl group, it preferably has 8 to 12 carbon atoms. Examples thereof include phenylvinyl and phenylpropenyl.
R1 is preferably an optionally substituted aryl group or an optionally substituted aralkyl group.
Examples of the substituents of these aryl, aralkyl, and alkenyl groups include alkyl groups such as methyl and ethyl, alkoxy groups such as methoxy, amino, alkylamino groups, acylamino groups, carboxyl, carboxylic ester groups, hydroxyl group, and halogen atoms such as chloro, besides the substituents given above.
In the case where R2 is an alkyl group having 1 to 10, preferably 1 to 8 carbon atoms, examples thereof include methyl, ethyl, propyl, butyl, and hexyl.
Preferred examples of R2 include methyl and propyl.
R3 is an optionally substituted bivalent hydrocarbon group having 1 to 20, preferably 1 to 12 carbon atoms. Examples thereof include methylene, ethylene, trimethylene, butylene, cyclohexylene, methylcyclohexylene, carboxycyclohexylene, norbornylene, vinylene, cyclohexenylene, phenylene, and naphthylene.
Preferred examples of R3 include ethylene, phenylene, and vinylene.
With respect to the proportions (mol %) of the structural units, that of a is 0xe2x89xa6axe2x89xa685, preferably 0xe2x89xa6axe2x89xa680; that of b is 0xe2x89xa6bxe2x89xa680, preferably 0xe2x89xa6bxe2x89xa670; the sum of a and b is not equal to 0; that of c is 0xe2x89xa6cxe2x89xa650, preferably 0xe2x89xa6cxe2x89xa645; that of d is 0xe2x89xa6dxe2x89xa630, preferably 0xe2x89xa6dxe2x89xa615; and that of e is 0xe2x89xa6exe2x89xa650, preferably 1xe2x89xa6exe2x89xa650.
A resin with smaller proportion of the structural acetal units having R1, i.e. with smaller a, tends to have an increased dielectric constant and a lowered Tg. In case where c is too large, the resin has enhanced hydrophilicity to show impaired performances due to moisture absorption, has an increased dielectric constant, and is hence less effective in improvements.
In case where d is too large, the resin has too small a proportion of acetal groups incorporated through acetalization and hence shows insufficient performances. In case where e is too small, the resin has reduced adhesiveness and is less effective in improvements. In case where e is too large, the resin has enhanced hydrophilicity to show impaired performances due to moisture absorption, has an increased dielectric constant, and is hence less effective in improvements.
In this specification, formula (Ixe2x80x2) is a structural formula which merely indicates the proportions of constituent elements of the resin and is not intended to specify an arrangement of these elements (e.g., a block arrangement). The modified polyvinyl acetal resin represented by formula (Ixe2x80x2) may contain other constituent elements as long as these optional elements do not defeat the objects of the invention.
The use amount of the modified polyvinyl acetal resin of ingredient (C) varies depending on purposes of the use thereof. However, too small addition amounts of the modified polyvinyl acetal resin result in the reduced ability to form a film on substrates. On the other hand, in case where the addition amount thereof is too large, the resultant composition has an increased viscosity and hence the solvent volatilizes insufficiently and partly remains in the film. The residual solvent may be causative of film blistering or peeling, depending on the subsequent heat history. Consequently, the incorporation amount of ingredient (C) is generally from 0.1 to 200 parts by weight, preferably from 0.5 to 180 parts by weight, per 100 parts by weight of the curable resin.
Provided as a preferred embodiment of the curable resin composition of the invention is a curable resin composition which comprises a curable resin (A), a curing agent (B), and a modified polyvinyl acetal resin (C) consisting essentially of repeating units represented by formula (I) wherein a, indicating the proportion of one kind of repeating units in the resin (C), satisfies 0xe2x89xa6axe2x89xa685. When the modified polyvinyl acetal resin is added to a combination of a curable resin and a curing agent, the curable resin composition obtained by mixing these ingredients has improved dielectric characteristics irrespective of the kind(s) of the curable resin and/or the curing agent.
The modified polyvinyl acetal resin has, as an essential component, substituents represented by R1 which are optionally substituted aryl groups, optionally substituted aralkyl groups, or optionally substituted alkenyl groups having an optionally substituted aryl group. An especially preferred range of the amount of these substituents is such that 10xe2x89xa6axe2x89xa680. A resin with smaller proportion of the structural acetal units having R1, i.e. with smaller a, tends to have an increased dielectric constant and a lowered Tg.
Examples of the curable resin of ingredient (A) include epoxy resins, acrylic compounds, isocyanate compounds, and melamine compounds. Preferred of these are epoxy resins from the standpoint of compatibility with the modified polyvinyl acetal resin of ingredient (C) and/or of the adhesiveness of the resin composition.
As the epoxy resins can be used various epoxy resins such as, e.g., bisphenol epoxyes, phenolic novolak epoxyes, cresol novolak epoxyes, glycidylamine epoxyes, alicyclic epoxyes, and glycidyl ester epoxyes. Preferred usable examples of bisphenol A epoxyes include xe2x80x9cEpikotexe2x80x9d 828, 1001, 1004, and 1009 (manufactured by Yuka Shell Epoxy K.K.), xe2x80x9cAralditexe2x80x9d GY250 and xe2x80x9cAralditexe2x80x9d 6071, 6072, 6097, and 6099 (manufactured by Ciba-Geigy Corp.), and xe2x80x9cDow Epoxyxe2x80x9d DER 331, 661, 664, and 669 (manufactured by The Dow Chemical Co.)
Preferred usable examples of the phenolic novolak epoxyes include xe2x80x9cEpikotexe2x80x9d 15 and 154 (manufactured by Yuka Shell Epoxy K.K.), xe2x80x9cAralditexe2x80x9d EPN 1138 and 1139 (manufactured by Ciba-Geigy Corp.), and xe2x80x9cDow Epoxyxe2x80x9d DEN 431, 438, and 485 (manufactured by The Dow Chemical Co.). Preferred usable examples of the cresol novolak epoxyes include xe2x80x9cAralditexe2x80x9d ECN 1235, 1273, and 1299 (manufactured by Ciba-Geigy Corp.) and xe2x80x9cEOCNxe2x80x9d 102 (manufactured by Nippon Kayaku Co., Ltd.). Preferred usable examples of the glycidylamine epoxyes include xe2x80x9cAralditexe2x80x9d MY 720 (manufactured by Ciba-Geigy Corp.) and xe2x80x9cSumiepoxyxe2x80x9d ELM 100, 120, and 434 (manufactured by Sumitomo Chemical Co., Ltd.).
Preferred usable examples of the alicyclic epoxyes include xe2x80x9cAralditexe2x80x9d CY 175, 177, and 179 (manufactured by Ciba-Geigy Corp.). Preferred usable examples of the glycidyl ester epoxyes include xe2x80x9cEpikotexe2x80x9d 190P and 191P (manufactured by Yuka Shell Epoxy K.K.) and xe2x80x9cAralditexe2x80x9d CY 184 and 192 (manufactured by Ciba-Geigy Corp.). Other usable epoxy resins include bisphenol F epoxyes such as xe2x80x9cAralditexe2x80x9d XPY 306 (manufactured by Ciba-Geigy Corp.) and brominated epoxyes such as xe2x80x9cEpikotexe2x80x9d 5050 and 5051 (manufactured by Yuka Shell Epoxy K.K.).
As the acrylic compounds can be used various acrylic compounds such as, e.g., acrylic or methacrylic esters of mono-or polyhydric alcohols, such as alkyl acrylates, alkyl methacrylates, and alkylene dimethacrylates, hydroxyl-containing acrylic or methacrylic esters such as hydroxyalkyl acrylates and hydroxyalkyl methacrylates, amino-containing acrylic or methacrylic esters such as aminoalkyl acrylates and aminoalkyl methacrylates, acrylic acid, and methacrylic acid. Specific examples of these acrylic compounds include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, isopropyl acrylate, isobutyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, styryl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, isopropyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, styryl methacrylate, ethylene dimethacrylate, glycidyl-methacrylate, 2-hydroxyethyl acrylate, 4-hydroxybutyl acrylate, 2-hydroxyethyl methacrylate, 2-aminoethyl acrylate, 2-aminoethyl methacrylate, and acrylic or methacrylic esters produced by causing any of the epoxy resins enumerated above to add acrylic or methacrylic acid. Basically, any acrylic compound may be used as long as one or more acrylic or methacrylic groups are present in the chemical molecular structure thereof.
Usable examples of the isocyanate compounds include toluene 2,4-diisocyanate, p-phenylene diisocyanate, and hexamethylene diisocyanate.
As the curing agent of ingredient (B) to be used in the invention is selected a curing agent which enables the curable resin of ingredient (A) to cure sufficiently.
In the case where ingredient (A) is an epoxy resin, usable examples of ingredient (B) include aromatic amines such as m-phenylenediamine, 4,4xe2x80x2-methylenedianiline, and diaminodiphenyl sulfone, aliphatic polyamines such as diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and diethylaminopropylamine, imidazole compounds such as 2-ethyl-4-methylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 1-aminoethyl-2-methylimidazole, 1-(cyanoethylaminoethyl)-2-methylimidazole, and 1-benzyl-2-methylimidazole, acid anhydrides such as maleic anhydride, phthalic anhydride, hexahydrophthalic anhydride, and methylnadic anhydride, phenol compounds, dicyandiamide, and BF3/amine complexes such as BF3/monoethylamine complex and BF3/piperidine complex.
These curing agents may be used alone or in combination of two or more thereof. A curing accelerator can be suitably used in combination with the curing agent.
Further, the curing agent is generally used in such an amount that the number of active hydrogen atoms contained in, e.g., the amino, imino or phenolic hydroxyl groups derived from the curing agent or the number of acid anhydride groups of the curing agent is nearly equivalent to the number of epoxy groups derived from the epoxy resin.
In the case where ingredient (A) is an acrylic compound, usable examples of ingredient (B) include peroxides such as benzoyl peroxide and cumene hydroperoxide and diazo compounds such as azobisisobutyronitrile.
Another preferred embodiment of the curable resin composition of the invention is the curable resin composition described above which comprises a curable resin (A), a curing agent (B), and a modified polyvinyl acetal resin (C) consisting essentially of repeating units represented by formula (Ixe2x80x2) and in which the curable resin (A) is an epoxy resin. In this case, when the modified polyvinyl acetal resin (C) is used in combination with an epoxy resin as the curable resin (A), the curable resin composition obtained by mixing these ingredients is improved in film-forming properties, flexibility, and adhesiveness irrespective of whether or not the modified polyvinyl acetal resin (C) has, in the structure thereof, groups represented by R1, i.e., optionally substituted aryl groups, optionally substituted aralkyl groups, or optionally substituted alkenyl groups having an optionally substituted aryl group.
As the epoxy resin in the embodiment shown above can be used various epoxy resins such as, e.g., bisphenol epoxyes, phenolic novolak epoxyes, cresol novolak epoxyes, glycidylamine epoxyes, alicyclic epoxyes, and glycidyl ester epoxyes. Preferred examples of these types of epoxyes include the epoxy compounds enumerated above.
On the other hand, ingredient (B) is, for example, an aromatic amine, alicyclic polyamine, imidazole compound, acid anhydride, phenol compound, dicyandiamide, or BF3/amine complex, such as those enumerated above.
These curing agents may be used alone or in combination of two or more thereof. A curing accelerator can be suitably used in combination with the curing agent.
Further, the curing agent is generally used in such an amount that the number of active hydrogen atoms contained in, e.g., the amino, imino or phenolic hydroxyl groups derived from the curing agent or the number of acid anhydride groups of the curing agent is nearly equivalent to the number of epoxy groups derived from the epoxy resin.
The resin composition of the invention, which contains the modified polyvinyl acetal resin, is suitable for use in electrical insulating materials, and is useful in anisotropic conductive films, interlayer dielectrics, or electronic members for high-speed communication apparatus, e.g., routers. On the other hand, the composition is applicable to other fields such as, e.g., adhesives, coating materials, linings, fiber-reinforced composites, and constructional materials so as to take advantage of properties thereof such as adhesiveness and film-forming properties.
Since the composition is highly compatible, it can be used in combination with a curable or plastic resin, e.g., an epoxy resin, acrylic resin, or urethane resin.
Inorganic or organic fibers and organic or inorganic fillers may be added to the composition as long as this addition does not reduce the performances of the composition.
Methods for curing the curable resin composition of the invention are not particularly limited as long as the curable resin can be sufficiently cured with the curing agent by the action of heat, light, ultraviolet, etc. When ingredient (A) is an epoxy resin, heating is usually employed. Curing conditions cannot be specified unconditionally because they vary depending on the kinds of the epoxy resin and curing agent. However, in the case of a combination of a bisphenol A epoxy resin and an imidazole curing agent, the curing temperature is generally from 10 to 200xc2x0 C. and the curing time is generally from 1 to 7 hours.
The curable resin composition of the invention may be applied to a substrate by the so-called wet process after having been mixed using a solvent. Alternatively, the composition may be applied to a substrate by the so-called hot-melt process after having been mixed without using a solvent optionally with heating. The substrate may be a plastic, metal, ceramic, or another substrate. Examples of the plastic include polyesters, polyamides, and polyimides. Examples of the metal include aluminum, copper, iron, stainless steel, and silicon. Examples of the ceramic include glasses and alumina. Examples of the polyimides among these materials include Kapton (trade name; manufactured by Toray Industries, Inc.) and Upilex (trade name; manufactured by Ube Industries, Ltd.). Of these, Upilex is especially preferred as the substrate.
Although the curable resin composition of the invention is suitable for use as an adhesive, inorganic or organic fibers or organic or inorganic fillers may be added thereto as long as this addition does not reduce the performances of the composition. The composition is applicable to other fields such as, e.g., coating materials, linings, electrical insulating materials, and constructional materials so as to take advantage of the adhesiveness and film-forming properties thereof.
The curable resin composition of the invention may be applied to a substrate by the so-called wet process after having been mixed using a solvent, or may be applied to a substrate by the so-called hot-melt process after having been mixed without using a solvent optionally with heating. Inorganic or organic fibers or organic or inorganic fillers may be added to this composition.
The substrate may be a plastic, metal, ceramic, or another substrate. Examples of the plastic include polyesters, polyamides, and polyimides. Examples of the metal include aluminum, copper, iron, stainless steel, and silicon. Examples of the ceramic include glasses and alumina. Examples of the polyimides among these materials include Kapton (trade name; manufactured by Toray Industries, Inc.) and Upilex (trade name; manufactured by Ube Industries, Ltd.). Of these, Upilex is especially preferred as the substrate.
(Laminated Product)
The laminated product of the invention comprises a substrate layer and a layer of the curable resin composition containing a modified polyvinyl acetal resin represented by formula (Ixe2x80x2) and/or a cured composition obtained by curing the composition.
Examples of processes for producing the laminated product include a method comprising coating a substrate with either a solution of the curable resin composition in a solvent or a melt of the composition and then curing the applied composition under given conditions. A three-layer laminated product composed of a substrate, an adhesive layer, and an adherend can be obtained by superposing the adherend on the surface of the thus-applied solution or melt of the uncured curable resin composition and then curing the composition. Furthermore, when fibers or an inorganic or organic filler is mixed with a solution or melt of the curable resin composition and the mixture is likewise applied to a substrate, then a laminated product having a cured composition united with the adherend can be obtained.
Since the laminated product of the invention has as a component thereof a layer of the curable resin composition and/or of a cured composition obtained by curing the composition and this layer has improved film-forming properties, there is a wide choice of substrates. Furthermore, since the curable resin composition can form a stable and homogeneous film having excellent adhesiveness to substrates and flexibility, a highly stable laminated product having especially high flexibility is obtained.